Metallized polyimide film containing a hydrocarbyl tin compound

ABSTRACT

A vacuum metallized polyimide film comprising an aromatic polyimide layer containing a hydrocarbyl tin compound in oxidation states (II) or (IV) as an additive and a metal plated layer bonded integrally with a high bonding strength or high adhesion through a vacuum deposited metal layer without the use of an adhesive. The metallized polyimide film can be used for flexible printed circuits and multilayer printed wiring boards, as well as for heaters, antennas and antistatic films.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum metallized polyimide film.More specifically, the invention relates to a vacuum metallizedpolyimide film comprising an aromatic polyimide layer and a metal layerbonded integrally, giving high bonding strength and high adhesion afterexposure to temperature and humidity aging. The metal layer is formedwithout the aid of an adhesive by vacuum deposition of a thin metallayer followed by ectroplating to the desired metal thickness. Themetalized polyimide film can be utilized for various purposes, such asfor flexible printed circuits and multilayer printed wiring boards,rigid-flex construction, and tape automated bonding, as well as forheaters, antennas and anti-static films.

2. Description of the Prior Art

Certain electronic assemblies have conductor traces on one or both sidesof a dielectric substrate. Preferred dielectrics for applicationsrequiring flexible substrates, especially in multilayer constructions,and tape automated bonding (TAB) involve the use of polyimide films. Ingeneral, the conductive layers on the polyimide film substrate areprovided through the use of metal foils and adhesives especiallyformulated for their physical and thermal stability. The conductivelayers are also provided, in some cases, through direct metallization byvacuum deposition or by electroless deposition methods well-known in theart.

The addition of small amounts of hydrocarbyl tin compounds and tin saltsinto the polyimide film has recently been disclosed in U.S. Pat. Nos.5,218,034 and 5,272,194, as improving adhesion when the polyimide filmis bonded to metal foils using an epoxy, acrylic or other heat-resistantadhesive. There is, however, no teaching or suggestion of the surprisingand unexpected adhesion improvement after exposure to temperaturehumidity aging provided by a metallized polyimide film formed bydirectly bonding a polyimide film layer containing a hydrocarbyl tincompound to a metal vacuum deposited layer without the use of anadhesive, as specifically claimed herein.

The adhesive bonding method has certain disadvantages, especially infine line applications, multilayer applications, and applicationsrequiring chemical milling, where either the properties of the adhesiveor the physical space occupied by the adhesive are limiting factors. Forexample, adhesively bonded polyimide film-metal laminates can exhibitpoor dimensional stability, a severe disadvantage for laying upmultilayer boards; or limited resolution, a disadvantage in making fineline circuits.

A preferred construction, especially in multilayer applications and fineline circuits such as TAB, would avoid the use of adhesives altogetherand provide the metal directly bonded to the polyimide film substrate.However, the durability of directly metallized polyimide film substratesalso poses significant problems.

Two methods for preparing adhesiveless metal coated polyimide filmslayer the related methods of evaporative and sputter deposition,followed by electrolytic copper buildup to obtain the desired thickness.Sputtering generally provides better adhesion than evaporativedeposition, but clads made with both techniques exhibit significant lossof adhesion when exposed to temperature humidity aging.

In order to improve the adhesive strength between the aromatic polyimidefilm and the metal layer, as described above, attempts have been made toroughen the surface of the polyimide film, or to introduce reactivefunctional groups by a corona discharge or plasma treatment, or by achemical surface treatment. Nevertheless, even when using such knownmethods, loss of adhesion occurs during temperature humidity aging.Thus, a need still exists for a metallized polyimide film, whicheliminates the aforesaid disadvantages, and which has a high adhesivestrength between the polyimide film layer and the vacuum deposited metallayer.

SUMMARY OF THE INVENTION

As hereinbefore set forth, the ability of a metal layer to retain anintimate bond to a polyimide film substrate after temperature humidityaging is a desirable feature in many electronic or electricalapplications. By utilizing the method of the present invention, it hasbeen found that a significant increase in the bonding properties may beobtained with a concomitant increase in the peel strength of a polyimidefilm directly bonded to a vacuum deposited metal layer. This increase,as will hereinafter be shown, is obtained by incorporation of specifichydrocarbyl tin compounds into the polyimide film.

In one aspect, an embodiment of this invention resides in a metallizedpolyimide film comprising (a) a polyimide film base layer containing ahydrocarbyl tin compound in oxidation states (II) or (IV), wherein theconcentration of tin in said polyimide film ranges from 0.02 to 1% byweight, (b) a thin, vacuum deposited metal layer on at least one side ofsaid polyimide film base layer, and (c) a metal plated layer appliedonto said vacuum deposited metal layer, wherein said polyimide baselayer is directly bonded to said vacuum deposited metal layer withoutthe use of an adhesive.

Another embodiment of the invention resides in a process for preparing ametallized polyimide film, comprising the steps of:

(a) incorporating a hydrocarbyl tin compound in oxidation states (II) or(IV) into a solution of a poly(amic acid) precursor of a polyimide film;

(b) forming a solidified self-supporting film of said poly(amic acid)precursor;

(c) heating said solidified poly(amic acid) film at a temperaturegreater than 350° C. to completely imidize said poly(amic acid) to formsaid polyimide film, wherein the concentration of tin in said completelyimidized polyimide film ranges from 0.02 to 1% by weight;

(d) forming a thin metal layer by vacuum deposition of a metal on atleast one side of said polyimide film; and

(e) applying a thick metal plated layer onto said vacuum deposited metallayer, wherein said polyimide base layer is directly bonded to saidvacuum deposited metal layer without the use of an adhesive.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a metallized polyimide film having animproved bond strength after temperature humidity aging between thepolyimide film layer and a metal layer formed by vacuum depositing athin metal layer followed by electroplating to the desired metalthickness. It has been found that a metallized polyimide film havingexcellent adhesion properties after temperature humidity aging can beobtained by incorporation of a minor amount of a hydrocarbyl tincompound in oxidation states (II) or (IV) into the polyimide film layer,and then effecting a vacuum deposition of a metal onto the surface ofthe polyimide film containing the hydrocarbyl tin compound and, further,effecting a metal plating on the vacuum deposited metal layer to therebyaccomplish the present invention.

According to the process of the present invention, a minor mount of ahydrocarbyl tin compound in oxidation states (II) or (IV) is added to asolution of a poly(amic acid) precursor in an organic solvent and thepoly(amic acid) converted to the corresponding polyimide by heating at atemperature greater than 350° C.

The polyimide films used in this invention can be made generally asdisclosed in U.S. Pat. Nos. 3,179,630 and 3,179,634, the disclosures ofwhich are hereby incorporated by reference. The poly(amic acids) aremade by dissolving substantially equimolar amounts of at least onearomatic tetracarboxylic dianhydride at least one aromatic diamine in anorganic solvent and agitating the resulting solution under controlledtemperature conditions until polymerization of the dianhydride and thediamine is completed.

Suitable dianhydrides for use in the polyimide films include:pyromellitic dianhydride; 2,3,6,7-naphthalene tetracarboxylicdianhydride; 3,3',4,4'-biphenyl tetracarboxylic dianhydride;1,2,5,6-naphthalene tetracarboxylic dianhydride; 2,2',3,3'-biphenyltetracarboxylic dianhydride; 3,3', 4,4'-benzophenone tetracarboxylicdianhydride; 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride;3,4,9,10-perylene tetracarboxylic dianhydride;2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride;1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride;1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride;bis(2,3-dicarboxyphenyl)methane dianhydride;bis(3,4-dicarboxyphenyl)methane dianhydride; oxydiphthalic dianhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride; and the like.

Suitable aromatic diamines for use in the polyimide films include:4,4'-diaminodiphenyl propane; 4,4'-diaminodiphenyl methane; benzidine;3,4'-dichlorobenzidine; 4,4'-diaminodiphenyl sulfide;3,4'-diaminodiphenyl sulfone; 4,4'-diaminodiphenyl sulfone;4,4'-diaminodiphenyl ether; 3,4'-diaminodiphenyl ether;1,5-diaminonaphthalene; 4,4'-diaminodiphenyldiethyl silane;4,4'-diaminodiphenyl silane; 4,4'-diaminodiphenyl ethyl phosphine oxide;4,4'-diaminodiphenyl N-methyl amine; 4,4'-diaminodiphenyl N-phenylamine; 1,4-diamino benzene (p-phenylene diamine); 1,3-diaminobenzene(m-phenylene diamine); 1,2-diaminobenzene(o-phenylene diamine);and the like.

The preferred polyimide film used in this invention is derived from4,4'-diaminodiphenyl ether and pyromellitic dianhydride.

Copolyimide films derived from any of the above diamines anddianhydrides can also be used. Particularly preferred copolyimide filmsare those derived from 15 to 85 mole % of biphenyltetracarboxylicdianhydride, 15 to 85 mole % of pyromellitic dianhydride, 30 to 100 mole% of p-phenylene diamine and 0 to 70 mole % of 4,4'-diamino diphenylether. Such copolyimide films are described in U.S. Pat. No. 4,778,872,which disclosure is also incorporated herein by reference.

The organic solvent must dissolve one or both of the polymerizingreactants and, preferably, should dissolve the poly(amic acid)polymerization product. The solvent must be substantially unreactivewith all of the polymerizing reactants and with the poly(amic acid)polymerization product.

Preferred organic solvents include normally liquidN,N-dialkylcarboxylamides, generally. Preferred solvents include thelower molecular weight members of such carboxylamides, particularlyN,N-dimethylformamide and N,N-dimethylacetamide. Other solvents whichmay be used are dimethylsulfoxide, N-methyl-2-pyrrolidone, tetramethylurea, dimethylsulfone, hexamethylphosphoramide, tetramethylene sulfone,and the like. The solvents can be used alone, in combinations with oneanother or in combinations with poor solvents such as benzene,benzonitrile, dioxane, and the like. The mount of solvent usedpreferably ranges from 75 to 90 weight % of the poly(amic acid)solution.

The poly(amic acid) solutions are generally made by dissolving thearomatic diamine in a dry solvent and slowly adding the aromatictetracarboxylic dianhydride under conditions of agitation and controlledtemperature in an inert atmosphere. The aromatic diamine is convenientlypresent as a 5 to 15 weight percent solution in the organic solvent andthe aromatic diamine and aromatic tetracarboxylic dianhydride areusually used in about equimolar amounts.

A minor amount of hydrocarbyl tin (II) or tin (IV) compound isintroduced, prior to the casting step, into the film-forming poly(amicacid) solution or while the polymerization of the poly(amic acid) isbeing performed.

The poly(amic acid) solution containing the organotin compound can becast as either a partially cured "gel film" or a "solvated film". Theterm "gel film" used herein means a sheet of the poly(amic acid) polymerwhich is laden with volatiles, primarily organic-solvent, to such anextent that the polymeric material is in a gel-swollen, plasticized,rubbery condition. The gel film thickness generally falls in the rangeof from 2 to 35 mils. The volatile content is usually in the range of 80to 90% by weight of the gel film. The gel film is self-supporting andpartially and incompletely cured, i.e., is at an intermediate stage ofcuring from the poly(amic acid) to the polyimide.

The gel film structure can be prepared by the chemical conversionprocess described in U.S. Pat. No. 3,410,826 by mixing a chemicalconverting agent and a tertiary amine, respectively, into the poly(amicacid) solution at a low temperature, followed by casting the poly(amicacid) solution in film form on a casting surface and then mildly heatingat, for example, 100° C. to activate the conversion agent and catalystfor transforming the cast film to a poly(amic acid)polyimide gel film.

The gel film is subsequently dried to remove the water, residual organicsolvent, and the remaining conversion chemicals, and the poly(amic acid)is completely converted to the polyimide. The drying can be conducted atrelatively mild conditions without complete conversion of the poly(amicacid) to the polyimide at that time, or the drying and conversion can beconducted at the same time using higher temperatures. Because the gelfilm has so much liquid which must be removed during the drying andconverting steps, it must be restrained during drying to avoid undesiredshrinkage. In continuous production, the film can be held at the edges,such as in a tenter frame using tenter clips or pins for restraint.

Preferably, high temperatures are used for short times to dry the filmand convert it to the polyimide in the same step. It is preferred toheat the film to a temperature of greater than 350° C., most preferably,greater than 400° C. for 15 to 400 seconds. During this drying andconverting process, the film is restrained from undue shrinking and, infact, can be stretched by as much as 200% of its initial dimension priorto completion of the drying and conversion. Stretching can be in anydirection. In film manufacture, stretching can be in either thelongitudinal direction or the transverse direction. If desired,restraint can also be provided to permit some limited degree ofshrinkage.

A "solvated film" of the poly(amic acid) is a film which is allpoly(amic acid) or which has only a low polyimide content, for example 0to 25%, and which is about 50 to 75% by weight polymer and 25 to 50% byweight solvent. Such film is sufficiently strong to be self-supporting.

The solvated poly(amic acid) can be prepared by casting the poly(amicacid) solution on a casting surface and heating at a temperature above50° C. to partially convert the poly(amic acid) to polyimide. The extentof poly(amic acid) conversion depends on the temperature employed andthe time of exposure, but, generally about 25 to 95% of the amic acidgroups are converted to imide groups. The partially converted poly(amicacid) is then thermally converted to the polyimide by heating attemperatures above 350° C., preferably above 400° C.

The polymide film contains from 0.02 to 1% by weight of tin based on theweight of the final cured polyimide film. When amounts of tin less than0.02% are used, little improvement in adhesive properties of thepolyimide film is obtained. Moreover, if the tin concentration exceeds1% by weight, the properties of the polyimide film may be compromised. Apreferred amount of tin present in the polyimide film ranges from 0.02to 0.7% by weight and, most preferably, from 0.05 to 0.50% by weight.

Although not wishing to be bound by any specific theory, it is believedthat the incorporation of the hydrocarbyl tin compound into thepolyimide film improves adhesion after temperature humidity agingthrough three different mechanisms. Firstly, the cohesive strength ofthe polyimide film is increased through additional crosslinking sitesprovided by the hydrocarbyl tin compound. The bonds between the organicand tin moieties are broken at the high temperatures used to cure thepolyimide film. The organic moieties are vaporized and the remaining tincenters either form coordination complexes with different polyimidechains and/or catalyze an interchain condensation leading to acrosslinked structure which increases the molecular weight and strengthof the polyimide film. Accordingly, a temperature greater than 350° C.,preferably greater than 400° C. is necessary to obtain the catalystactivation and achieve the desired strength improvement. Secondly, thetin centers also segregate to the near surface region of the polyimidefilm at the high temperatures used for curing. The resultingcompositional gradient is believed to produce a gradient in the physicaland mechanical properties of the film (e.g. modulus, glass transitiontemperature, thermal expansion etc.) which reduces the abrupt variationof these properties that normally occurs between the tin and thepolyimide interface. Finally, the tin centers in the near surface regionact as sources for the formation of either alloys or intermetalliccompounds with the metal deposited onto the polyimide film, especiallyunder higher temperature conditions where the metal diffuses into thepolyimide film.

Any hydrocarbyl tin compound in oxidation states (II) or (IV) such as:

dibutyltin diacetate

dibutyltin dilaurate

bis(tributyltin)oxide

tributyltin acetate

tetrabutyltin

tetraphenyltin

tributyltin chloride

dibutyltin chloride

can be incorporated into the polyimide film.

Different hydrocarbyl tin compounds, which have differentcharacteristics and properties due to the different organic moieties,may be used. For example, a hydrocarbyl tin compound having an organicmoiety generated by-product can be selected which is inert or compatiblewith the process environment, or a liquid, e.g. bis(tributyltin)oxidecan be used instead of a powder, e.g. tributyltin acetate. Furthermore,different hydrocarbyl tin compounds can have different reactioncharacteristics when incorporated into the poly(amic acid) solution.Dibutyltin diacetate accelerates the gelation rate of the poly(amicacid) and reduces the processing time, whereas bis(tributyltin)oxide ortetrabutyl tin do not affect the processing characteristics of thepoly(amic acid) solution and may be added either prior to or during thepoly(amic acid) polymerization.

A particularly preferred hydrocarbyl tin compound isbis(tributyltin)oxide which when used in a concentration range of from0.2 to 0.7 weight % provides a peel strength after temperature humidityaging of at least 4.5 pli when the polyimide film is directly bonded toa metal vacuum deposited layer.

The polyimide film can additionally contain small mounts of fineparticulate fillers to impart slip and handling or other desirableproperties to the film. Such particulate fillers include, but are notlimited to, silica, alumina, silicates, calcium phosphates and the like.Calcium hydrogen phosphate is a particularly preferred particulatefiller and when used in an amount of from 100 to 2000 ppm providesadvantageous slip properties to the polyimide film.

The polyimide film can have any thickness suitable for use as asubstrate for electronic circuitry, and most generally is in the form ofa relatively thin film having a thickness of between about 10 and 125micrometers.

According to the process for preparing the metallized polyimide film, ametal, such as a noble metal, alkaline earth metal, or transition metal(e.g. copper, cobalt, nickel, chromium, titanium) is vacuum deposited byan evaporative deposition method or the sputtering method on the surfaceof the polyimide film containing the hydrocarbyl tin compound to form athin metal layer. The vacuum deposited metal layer is preferably ahomogeneous layer having a thickness of about 500 to 5000 Angstroms,more preferably about 1000 to 2000 Angstroms.

In the above vacuum deposition method, the vacuum pressure preferablyranges from 1×10⁻¹⁰ to 5×10⁻² Torr and the deposition temperature rangesfrom 20° C. to 200° C.

Among the above methods that can be used, the DC or RF Magnetronsputtering methods are particularly preferred and, preferably, thevacuum pressure used during sputter deposition can range from 1×10⁻³ to8×10⁻² Torr and the sputter deposition temperature can range from 20° C.to 200° C.

A metal plated layer is subsequently applied to the thin vacuumdeposited metal layer by an electroplating method to thereby form athick metal plated layer and thus provide a metallized polyimide film.

The thick metal plated layer may be, for example, a layer of a metalsuch as copper, nickel, chromium, zinc, cadmium, tin, lead, gold,silver, cobalt, palladium, platinum, aluminum and can have a thicknessranging from 10 to 70 micrometers, preferably from 15 to 35 micrometers.

An electroplating method can be used wherein the film article to beplated is dipped as the cathode into a solution containing metal ions,an anode is dipped opposite thereto and a direct current is passedtherebetween to form a metal coated layer.

As metal electroplating conditions, the plating bath preferably containscopper sulfate, sulfuric acid, chloride ion, and brightener and theplating conditions are, preferably, a temperature of 20° C. to 25° C.and a current density of 10 amps/ft². Prior to electroplating, thevacuum deposited layer can be cleaned with VersaCLEAN® 470 precleaner.

Another useful metal layer forming method that can be used in theformation of the metallized polyimide film involves first forming atie-coat layer of metal such as chromium, nickel, or titanium on thepolyimide film surface. Such tie-coat layers can have thicknessesranging from 10 to 300 Angstroms and aid in bonding the metal vacuumdeposited layer to the polyimide film.

An improvement in peel strength can also be obtained by treating thepolyimide film in a gas plasma prior to vacuum deposition of the metalon the surface of the polyimide. A gas plasma is formed by theinteraction of a gas with an electrical field. For example, anelectrical field may be provided by a RF generator which provides thenecessary field for interaction with a gas to produce radical speciesprimarily by electron-induced dissociation. These species then interactwith the outermost atomic layers of the polyimide film, whereby astronger bond with the subsequently vacuum deposited metal can beachieved.

Examples of gases which can be used to form the gas plasma include inertgases such as helium, argon, krypton, xenon, neon, radon, nitrogen,etc., as well as other gases such as oxygen, air, carbon monoxide,carbon dioxide, carbon tetrachloride, chloroform, hydrogen, etc.,fluorinated gases (commonly known as Freons®) including carbontetrafluoride, dichlorodifluoromethane trifluorochloromethane,trichlorofluoromethane as well as mixtures of the aforesaid gases.Preferred gases include oxygen and argon and blends of oxygen and argon.

The pressure of the gas in the plasma atmosphere should be in the rangefrom 1×10⁻³ to 5×10⁻¹ Torr or, preferably, from 1×10⁻² to 8×10⁻² Torr,and the temperature may range from ambient (20° C. to 25° C.) up to theglass transition or melting temperature of the polyimide polymer. Theelectric power can be supplied from various sources such as by directcurrent, alternating current, audio frequency, intermediate frequency,microwave frequency, etc. The power density employed is the electricpower per unit area and ranges from 10 to 500 mW/cm². The treatment ofthe polyimide film with a gas plasma is effected for a period of timeranging from about 5 seconds up to about 30 minutes or more in duration,the time of treatment depending upon the other operating conditionsincluding temperature, pressure and power density. The vacuum depositionof metal on the surface of the polyimide film can be effectedimmediately after the gas plasma treatment.

In general, metallized polyimide films which are formed by plating ametal onto a plasma treated vacuum metallized polyimide film have goodinitial adhesion for many applications. The peel strength of many suchmetallized polyimide films currently in use is generally insufficientfor many end uses because any delamination can cause the failure of themetallized film to operate in its intended use. However, even the peelstrength currently achievable in many metallized polyimide films can bedecreased by exposure of the metallized polyimide film to processingchemicals (e.g. etchants, cleaners, coatings, etc.) and environmentalstress (e.g. humidity) and can be reduced to less than 4 pounds per inchand, in some cases, to less than 2 pounds per inch. As a result,conventional metallized polyimide films, due to low peel strengths afterenvironmental testing, can fall to function satisfactorily in circuitassemblies on printed wiring boards.

The metallized polyimide film of the invention has a metal plated layerand a polyimide film layer, containing an adhesion-enhancing amount of ahydrocarbyl tin compound in oxidation states (II) or (IV), bondeddirectly and integrally with a high bonding strength after acceleratedaging, without an adhesive layer, through a metal vacuum deposited layerand can advantageously be used as a two layer clad for making printedcircuits. The peel strength after temperature humidity aging of themetallized polyimide film can be greater than about 4.5 pounds per inchand can be in excess of 7 pounds per inch.

The advantageous properties of this invention can be observed byreference to the following examples which illustrate, but do not limit,the invention.

EXAMPLES 1 to 3 (COMPARATIVE EXAMPLES 1A to 3A)

Pyromellitic dianhydride was added to a solution of 4,4'-diaminodiphenylether in N,N-dimethylacetamide until the solution viscosity was 2000 to3000 poises and the percent solids was approximately 20%. The resultingpoly(amic acid) solution was cooled and, prior to casting, mixed withexcess molar quantities of acetic anhydride and 3-methyl pyridine.Bis(tributyltin)oxide (1200 ppm) was added to Examples 1 to 3 as a 2%solution in N,N-dimethylacetamide, whereas no bis(tributyltin)oxide wasadded to Comparative Examples 1A to 3A. Polyimide films containing tinare designated as HZT and Comparative films are designated as H. Thepoly(amic acid) solution was cast onto a heated surface and fastened atthe edges to a tenter chain and transported through an oven to dry thefilm and complete the imidization. A temperature of at least 400° C. wasused in the oven to produce the final cured polyimide film.

The polyimide films of Examples 1 and 2 and Comparative Examples 1A and2A were cut into approximately 12 inch squares and rinsed with Freon®.The samples were placed in a Leybold L560 electron beam evaporator. Avacuum deposited layer of copper having a thickness of approximately2000 Angstroms was then formed directly on the surface of the polyimidefilms using electron beam heating. The vacuum deposition was conductedat a pressure of 2.2×10⁻⁶ Torr.

When plasma treatment was used prior to vacuum metal deposition (Example2 and Comparative Example 2A), gas was first introduced into the chamberto a pressure of 6×10⁻² Torr. The plasma treatment was conducted at anestimated power density of 160-200 mW/cm². Plasma etching was conductedfor 10 minutes, the voltage was turned off, the dosing valve closed andthe chamber pumped down to 2.2×10⁻⁶ Torr.

A thick (35 micrometers) copper plated layer was then formed on thevacuum deposited layer of the polyimide film. The copper plating wasconducted using a Copper Pro® 250 plating bath (from E. I. duPont deNemours and Co.) comprising copper sulfate, sulfuric acid, chloride ionand brighteners at a current density of 10 amps/ft².

The metallized polyimide films were then aged for 500 hours at 85° C.and 85% relative humidity. The peel strength of the metal plated filmsafter 500 hours was determined according to IPC Test Method 2.4.9,Revision C, using 0.5 inch wide strips.

The polyimide films of Examples 3 and Comparative Example 3A were cutinto approximately 1.75 inch squares and rinsed with Freon®. The sampleswere placed in a Balzers BNAE080-T thin film deposition chamber. Avacuum deposited layer of copper having a thickness of approximately2000 Angstroms was then formed directly on the surface of the polyimidefilms using a resistive heating means. The vacuum deposition wasconducted at a pressure of 1 to 3×10⁻⁶ Torr for such time until thethickness of the vacuum deposited copper layer was 2000 Angstroms.

Plasma treatment was used prior to vacuum metal deposition, and gas wasfirst introduced into the chamber by a gas dosing valve to a pressure of5 to 7×10⁻² Torr. The plasma was then started using a voltage of from100 to 250 volts at 2 ma corresponding to a power density of from 10 to25 mW/cm². Plasma etching was performed for 5 minutes, the voltage wasturned off, the dosing valve closed and the chamber pumped down to 1 to3×10⁻⁶ Torr.

The copper plating 3tep was the same as for Examples 1 and 2 andComparative Examples 1A and 2A. Aging at 85° C./85% relative humiditywas performed in a temperature/humidity chamber and peel testing,because of the small sample size, was a modification of IPC Test Method2.4.9, Revision C. The 0.5 inch wide strips were pulled at a crossheadspeed of 0.5 inch per minute over a distance of 0.75 inch withcalculation of the peel value over the last 0.5 inch.

The peel values for Examples 1 to 3 and Comparative Examples 1A to 3Aare summarized in Table I.

                  TABLE I                                                         ______________________________________                                                Polyimide                                                             Example Film Type.sup.1                                                                             Organotin  Metal                                        No.     Thickness (μm)                                                                           Additive.sup.2                                                                           Evaporated.sup.3                             ______________________________________                                        1       HZT      (50)     Yes      Cu                                         1A      H        (75)     No       Cu                                         2       HZT      (50)     Yes      Cu                                         2A      H        (75)     No       Cu                                         3       HZT      (50)     Yes      Cu                                         3A      H        (75)     No       Cu                                         ______________________________________                                        Example    Plasma    500 Hrs @ 85° C./85% RH                           No.        Treatment Peel Strength (pli).sup.4                                ______________________________________                                        1          None      5.22                                                     1A         None      1.84                                                     2          Argon     6.57                                                     2A         Argon     2.69                                                     3          Oxygen    5.22                                                     3A         Oxygen    1.70                                                     ______________________________________                                         .sup.1 H = pyromellitic dianhydride, 4,4diaminodiphenyl ether                 .sup.2 Contains 1200 ppm bis(tributyltin)oxide                                .sup.3 2000 Angstroms                                                         .sup.4 Examples 3 and 3A based on 0.5 inch pull                          

EXAMPLES 4 to 6 (COMPARATIVE EXAMPLES 4A to 6A)

The polyimide films of Examples 4 to 6 were made in the same manner asExamples 1 to 3, except that finely divided particles of calciumhydrogen phosphate (1200 to 1500 ppm) were added to provide slipproperties to the final film. The polyimide films of ComparativeExamples 4A to 6A were also made in the same manner as ComparativeExamples 1A to 3A, except that finely divided particles of calciumhydrogen phosphate (1200 to 1500 ppm) were added to provide slipproperties to the final film. Polyimide films containing tin and slipadditive are designated HNZT and Comparative slip additive containingfilms are designated HN. The plasma treating conditions and vacuumcopper deposition used in Examples 4 to 6 and Comparative Examples 4A to6A are the same as those used in Example 3 and Comparative Example 3A. Athin (10 Angstroms) or thick (300 Angstroms) layer of chromium wasevaporatively deposited prior to vacuum copper deposition. The vacuumdeposited metallized polyimide films were plated to a thickness of 35 μmwith copper, temperature/humidity aged for 500 hours and peel tested thesame as for Example 3 and Comparative Example 3A. All of the tincontaining polyimide films broke while trying to start a peel indicatinga peel strength of 6 pli or greater. The peel strength results aresummarized in Table II.

                  TABLE II                                                        ______________________________________                                        Ex-   Polyimide                                                               ample Film Type.sup.1                                                                           Organotin Metal    Chromium                                 No.   Thickness (μm)                                                                         Additive.sup.2                                                                          Evaporated.sup.3                                                                       Tie Layer.sup.4                          ______________________________________                                        4     HNZT    (75)    Yes     Cu       300                                    4A    HN      (75)    No      Cu       300                                    5     HNZT    (75)    Yes     Cu       10/Air.sup.5                           5A    HN      (75)    No      Cu       10/Air.sup.5                           6     HNZT    (75)    Yes     Cu        10                                    6A    HN      (75)    No      Cu        10                                    ______________________________________                                        Example  Plasma      500 Hrs @ 85° C./85% RH                           No.      Treatment   Peel Strength.sup.6                                      ______________________________________                                        4        Argon/Oxygen                                                                              KB.sup.7                                                 4A       Argon/Oxygen                                                                              1.41                                                     5        None        KB.sup.7                                                 5A       None        0.59                                                     6        Argon/Oxygen                                                                              KB.sup.7                                                 6A       Argon/Oxygen                                                                              2.42                                                     ______________________________________                                         .sup.1 HN = Pyromellitic dianhydride, 4,4diaminodiphenyl ether containing     1200 to 1500 ppm calcium hydrogen phosphate                                   .sup.2 Contains 1200 ppm bis(tributyltin)oxide                                .sup.3 2000 Angstroms                                                         .sup.4 Thickness of chromium tie layer in Angstroms                           .sup.5 Exposed to ambient conditions of 20-25° C. for 7 days after     chromium deposition                                                           .sup.6 Examples 4, 4A, 5, 5A, 6 and 6A based on 0.5 inch pull                 .sup.7 KB = film broke trying to start peel                              

EXAMPLES 7 to 10 (COMPARATIVE EXAMPLES 7A to 10A)

The polyimide films of Examples 7 to 10 and Comparative Examples 7A to10A contained 40% 3,3',4,4'-biphenyltetracarboxylic dianhydride, 60%pyromellitic dianhydride, 60% p-phenylenediamine and 40%4,4'-diaminodiphenyl ether. Poly(amic acid)s of approximately 15% solidsand 2000 to 3000 poises were converted, dried and cured in a mannersimilar to Examples 1 to 3 and Comparative Examples 1A to 3A. The amountof bis(tributyltin)oxide used in Examples 7 to 10 was 3500 ppm and wasadded as a 2% solution in N,N-dimethylaceteamide. The Examplescontaining tin are designated as EZT and the Comparative Examples aredesignated as E. Example 7 and Comparative Example 7A were metallized,aged and peel tested using the same conditions used for Examples 1 and 2and Comparative Examples 1A and 2A. Examples 8 and 9 and ComparativeExamples 8A and 9A were metallized, aged and peel tested using the sameconditions used for Example 3 and Comparative Example 3A. The vacuummetallization used in Example 10 and Comparative Example 10A was sputterdeposition. The films were plasma etched at 1.6×10⁻² Torr and a powerdensity of 150 to 160 mW/cm² for 10 minutes. The chromium was sputterdeposited at a pressure of 1.3×10⁻² Torr at 50 Angstroms/minute using apower of 650 watts. The copper was sputter deposited at a pressure of1.3×10⁻² Torr at 1000 Angstroms/minute using 5Kw for 2 minutes. Thevacuum deposited samples were plated, aged and peel tested in the samemanner as Examples 1 and 2 and Comparative Examples 1A and 2A. The peelvalues are given in Table III.

                  TABLE III                                                       ______________________________________                                                Polyimide                                                             Example Film Type.sup.1                                                                             Organotin  Metal                                        No.     Thickness (μm)                                                                           Additive.sup.2                                                                           Evaporated.sup.3                             ______________________________________                                        7       EZT      (50)     Yes      Cu                                         7A      E        (50)     No       Cu                                         8       EZT      (50)     Yes      Cu                                         8A      E        (50)     No       Cu                                         9       EZT      (50)     Yes      Cu                                         9A      E        (50)     No       Cu                                         10      EZT      (50)     Yes      Cr/Cu.sup.4                                10A     E        (50)     No       Cr/Cu.sup.4                                ______________________________________                                        Example   Plasma    500 Hrs.sup.5 @ 85° C./85% RH                      No.       Treatment Peel Strength (pli).sup.6                                 ______________________________________                                        7         None      5.45                                                      7A        None      3.25                                                      8         Argon     6.47                                                      8A        Argon     4.15                                                      9         Oxygen    7.00                                                      9A        Oxygen    3.20                                                      10        Argon     4.77                                                      10a       Argon     2.13                                                      ______________________________________                                         .sup.1 E = 3,3',4,4biphenyltetracarboxylic dianhydride, pyromellitic          dianhydride, pphenylenediamine, 4,4diaminodiphenyl ether.                     .sup.2 Contains 3500 ppm bis(tributyltin)oxide                                .sup.3 2000 Angstroms Cu.                                                     .sup.4 Examples 10 and 10A sputter deposited metal consisting of 150          Angstroms chromium followed by 2000 Angstroms of copper.                      .sup.5 Examples 10 and 10A temperature/humidity aged for 250 hrs.             .sup.6 Examples 8, 8A, 9 and 9A based on 0.5 inch pull.                  

What is claimed is:
 1. A metallized polyimide film comprising:(a) apolyimide film base layer containing a hydrocarbyl tin compound inoxidation states (II) or (IV), wherein the concentration of tin in saidpolyimide film ranges from 0.05 to 0.50% by weight; (b) a vacuumdeposited metal layer having thickness of from 500 to 5000 Angstroms onat least one side of said polyimide film base layer; and (c) anelectroplated metal layer having a thickness of from 10 to 70micrometers applied onto said vacuum deposited metal layer, wherein saidpolyimide base layer is directly bonded to said vacuum deposited metallayer without the use of an adhesive.
 2. The metallized polyimide filmof claim 1 wherein the polyimide film comprises pyromellitic dianhydrideand 4,4'-diaminodiphenyl ether.
 3. The metallized polyimide film ofclaim 1 wherein the hydrocarbyl tin compound comprisesbis(tributyltin)oxide.
 4. The metallized polyimide film of claim 1wherein the polyimide film comprises from 15 to 85 mole % of3,3',4,4'-biphenyltetracarboxylic dianhydride, 15 to 85 mole % ofpyromellitic dianhydride, 30 to 100 mole % of p-phenylene diamine and 0to 70 mole % of 4,4'-diamino-diphenyl ether.
 5. The metallized polyimidefilm of claim 4 wherein the polyimide film comprises 30 to 40 mole % of3,3',4,4'-biphenyltetracarboxylic dianhydride, 60 to 70 mole % ofpyromellitic dianhydride, 60 to 70 mole % of p-phenylenediamine and 30to 40 mole % of 4,4'-diaminodiphenyl ether.
 6. The metallized polyimidefilm of claim 1 wherein the thickness of the polyimide base film layerranges from 10 to 125 micrometers.
 7. The metallized polyimide film ofclaim 1 wherein the vacuum deposited metal layer is selected from thegroup consisting of noble metals, alkaline earth metals, and transitionmetals.
 8. The metallized polyimide film of claim 7 wherein the vacuumdeposited metal layer comprises copper.
 9. The metallized polyimide filmof claim 1 wherein the vacuum deposited metal layer is deposited byevaporation or sputter deposition.
 10. The metallized polyimide film ofclaim 1 wherein the electroplated metal layer is selected from the groupconsisting of copper, nickel, chromium, zinc, cadmium, tin, lead, gold,silver, cobalt, palladium, platinum and aluminum.
 11. The metallizedpolyimide film of claim 10 wherein the electroplated metal layercomprises copper.
 12. A metallized polyimide film comprising:(a) apolyimide film base layer comprising pyromellitic dianhydride and4,4'-diaminodiphenyl ether and bis(tributyltin)oxide, wherein theconcentration of tin in said polyimide film ranges from 0.05 to 0.50% byweight; (b) a vacuum deposited metal layer having a thickness of from500 to 5000 Angstroms on at least one side of said polyimide film baselayer; and (c) an electroplated metal layer having a thickness of from10 to 70 micrometers on said vacuum deposited metal layer, wherein saidpolyimide film base layer is directly bonded to said vacuum depositedmetal layer with a peel strength after aging for at least 500 hours at85% RH and 85° C. of at least 4.5 pli according to IPC Method 2.4.9,Revision C, without the use of an adhesive.
 13. A metallized polyimidefilm comprising:(a) a polyimide film base layer comprising3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride,p-phenylene diamine and 4,4'-diaminodiphenyl ether andbis(tributyltin)oxide, wherein the concentration of tin in saidpolyimide film ranges from 0.05 to 0.50% by weight; (b) a vacuumdeposited metal layer having a thickness of from 500 to 5000 Angstromson at least one side of said polyimide film base layer; and (c) anelectroplated metal layer having a thickness of from 10 to 70micrometers on said vacuum deposited metal layer, wherein said polyimidefilm base layer is directly bonded to said vacuum deposited metal layerwith a peel strength after aging for at least 500 hours at 85% RH and85° C. of at least 4.5 pli according to IPC Method 2.4.9, Revision C,without the use of an adhesive.